Matching layer systems and methods for ultrasound transducers

Abstract

Castable matching layers having a desired acoustic impedance are formed with hafnium compounds. For example, a low sound velocity matching layer with an acoustic impedance of about 5 MRayl is formed by mixing hafnia (HfO 2 ) powder with a casting resin. The matching layer is used for low frequency operation, such as operation at four or fewer megahertz, while providing a matching layer with a thickness of 150 microns or less for easy dicing. Since a maximum dicing blade exposure to blade thickness ratio is about 30 to 1, higher velocity matching layers may lead to dicing depths requiring thicker dicing blades. By using hafnium compounds, a lesser thickness may be provided, avoiding a reduction in sensitivity and mechanical stability due to wider kerfs resulting from thicker dicing blades. Other thicknesses, frequencies, acoustic impedances or other characteristics may be provided.

1 . In a matching layer of an ultrasound transducer, the matching layer including a resin, an improvement comprising: 
 a hafnium filler.    
   
   
       2 . The improvement of  claim 1  wherein the hafnium filler comprises hafnia powder.  
   
   
       3 . The improvement of  claim 1  wherein the hafnium filler comprises only particles of less than 7 microns maximum dimension and the matching layer has an acoustic impedance of about 3-8 MRayl.  
   
   
       4 . The improvement of  claim 3  wherein the particles are less than 1 micron and the acoustic impedance is less than about 4 MRayl.  
   
   
       5 . The improvement of  claim 3  wherein the particles are greater than 5 microns and the acoustic impedance is greater than about 6 MRayl.  
   
   
       6 . The improvement of  claim 3  wherein the acoustic impedance is about 5 MRayl.  
   
   
       7 . The improvement of  claim 1  wherein the hafnium filler comprises 10-40% by volume of the matching layer.  
   
   
       8 . The improvement of  claim 7  wherein the hafnium filler comprises 15-25% by volume of the matching layer.  
   
   
       9 . The improvement of  claim 1  wherein the matching layer has an ultrasound strip velocity of about 1600-1900 meters per second.  
   
   
       10 . The improvement of  claim 9  wherein the matching layer has an ultrasound strip velocity of about 1750 meters per second.  
   
   
       11 . The improvement of  claim 1  further comprising: 
 the matching layer being an intermediate matching layer between an upper matching layer and a lower matching layer.    
   
   
       12 . The improvement of  claim 1  wherein the matching layer has a maximum thickness of less than about 150 microns.  
   
   
       13 . The improvement of  claim 1  wherein the resin with the filler comprises a castable material.  
   
   
       14 . A method of manufacturing an ultrasound transducer with acoustic matching, the method comprising: 
 (a) loading a resin with a hafnium compound;    (b) casting the loaded resin with the hafnium compound; and    (c) positioning the cast material as a matching layer on the ultrasound transducer.    
   
   
       15 . The method of  claim 14  wherein (a) comprises loading with hafnia powder at about 10-40% by volume.  
   
   
       16 . The method of  claim 15  wherein (a) comprises loading with hafnia powder at about 15-25% by volume.  
   
   
       17 . The method of  claim 15  wherein the hafnium compound comprises only hafnia particles of less than 7 microns maximum dimension and that the cast material has an acoustic impedance of about 3-8 MRayl.  
   
   
       18 . The method of  claim 15  wherein the cast material has an ultrasound strip velocity of about 1600-1900 meters per second.  
   
   
       19 . The method of  claim 15  wherein (c) comprises positioning the cast material between an upper matching layer and a lower matching layer.  
   
   
       20 . An ultrasound transducer for acoustic use adjacent to tissue, the ultrasound transducer comprising: 
 a transducer element; and    an acoustic impedance matching layer adjacent the transducer element, the matching layer containing a hafnium compound.